This invention relates to methods of forming physical vapor deposition targets and sputter deposition targets, to targets produced by such methods, to films produced by such targets, and, additionally, to targets independent of their method of formation.
Germanium selenide is a member of the chalcogenide class of compounds. Films of these compounds have been used in the manufacture of computer memory devices. Memory densities in excess of 340 Mbits/cm2 have been demonstrated with germanium selenide films with a minimum single layer feature size of approximately 0.18 micrometers.
Chalcogenides are finding utility in the manufacture of programmable metallization cells which have the potential for playing a significant role in future generations of computer memories. Thus, efficient formation of germanium selenide films with known and reproducable stoichiometries is an important goal. Germanium selenide films are typically formed by co-sputtering pure germanium and pure selenium targets. Simultaneous sputtering of both targets is carried out with simultaneous deposit of Ge and Se onto a common substrate, thereby creating a film containing both germanium and selenium.
However, the co-sputtering formation of germanium selenide films requires complex sputtering equipment, increasing processing costs. Also, precise control of two separate sputtering processes to achieve adequate film homogeneity, film uniformity, and film stoichiometry. Achieving such objectives in a production environment, as opposed to a laboratory environment, presents a significant and costly challenge.
According to one aspect of the invention, a method includes combining a solid first material and a solid second material and melting at least a portion of the first material sufficient to coat the second material and any remaining first material. The melted portion can define a first material liquid phase. An approximately homogenous distribution of the second material can be formed throughout the first material liquid phase. The first material liquid phase can be solidified to define a composite target blank that includes an approximately homogenous distribution of the second solid material in a matrix of the solidified first material. As an example, the first and second materials can include metals. The first material can comprise Se and the second material can comprise Ge. The melting of at least a portion of the first material and the forming of an approximately homogenous distribution can occur together and be accomplished by hot pressing. The composite target blank can include at least about 50 volume % (vol %) matrix. The melting can occur in a vessel while heating and compressing the first material. In such case, the first material liquid phase can exhibit a sufficiently high viscosity to prevent a substantial amount of the first material liquid phase from escaping the vessel during compression. Similarly, the viscosity of the first material liquid phase can prevent a substantial amount of second material from settling out of the approximately homogenous distribution in the first material liquid phase. By such methods, a composite target blank can be obtained that exhibits a bulk density of at least about 95% of theoretical density.
According to a further aspect of the invention, a sputter deposition target forming method can include combining a first powder comprising a first metal with a second powder comprising a second metal. The first metal can exhibit a melting point at least about 100 Celsius (xc2x0 C.) less than a melting point exhibited by the second metal. Heat and pressure can be applied to a first volume including the combined first and second powders, changing the first volume to a second volume. The second volume can include at least about 50 vol % liquid phase of the first metal. The second volume may be cooled into a composite target blank having an approximately homogenous distribution of at least the second powder. The first and second powders can exhibit particle sizes no greater than about 325 mesh. Also, the method can further include screening the first and second powders with a 100 mesh screen to separate agglomerations. The applying heat and pressure can include heating to a temperature of less than about the melting point of the second metal at a rate of from about 200 to about 400xc2x0 C. per hour while under compression of from about 6.9xc3x97106 to about 28xc3x97106 Pascals (about 1,000 to about 4,000 pounds/inch2). Also, the cooling of the second volume can include removing heat to obtain about an intermediate temperature, maintaining about the intermediate temperature for from about 45 to about 90 minutes, and cooling further to a room temperature of from about 20 to about 25xc2x0 C. The intermediate temperature can be about 200xc2x0 C. Also, the applying heat can attain a temperature of about 225xc2x0 C. The first powder can include at least about 99.99 weight % (wt %) Se on a metals basis and the second powder can include at least about 99.99 wt % Ge on a metals basis. The composite target blank can further exhibit a bulk density of at least about 98% of theoretical density.
In another aspect of the invention, a composite material can include a matrix of a first material and an approximately homogenous distribution of particles of a second material throughout the first material matrix. Also, a physical vapor deposition target can include at least about 50 vol % matrix and an approximately homogenous distribution of a powder throughout the matrix. The matrix can include a first metal and the powder can include a second metal. Still further, a sputter deposition target can include a continuous matrix of Se encapsulating an approximately homogenous distribution of a powder throughout the Se matrix. The powder can comprise at least about 99.99 wt % Ge on a metals basis. The target can comprise from about 25 to about 50 wt % Ge in the Se matrix.